Aqueous solutions of certain melamine-aldehyde polymers are known to have a wide variety of industrial uses. For example, the desired polymer, sometimes referred to as "active" melamine-aldehyde "resin," is applied to various fabrics to impart a permanent press characteristic to the fabric. The resin is also used in connection with the manufacture of paper products, although this practice has declined in recent years due in part to the problem of free aldehyde in the resin. The resin is known to improve the strength and resiliency of paper products. Melamine-aldehyde resins are also commonly used as flocculating agents in the treatment of wastewater. However, the presence of free aldehyde in the resin creates an additional problem in wastewater treatment. Such resins are also used as "detackifiers" in aqueous systems used to control paint overspray. Resins are also used to form microscopic capsules used in self-contained pressure sensitive copying materials. In each of these uses the presence of free aldehyde creates a problem in the use of the melamine-aldehyde resin. The free aldehyde may have a deleterious effect on the material being treated by the resin, may impart an undesirable odor to the material being treated, and may cause an environmental problem when free aldehyde ends up in process by-products, or in wastewater treated with resin.
The prior art has addressed the free aldehyde problem for a variety of uses of melamine-aldehyde resin. However, most existing methods for removing or destroying free aldehyde involve treatment of the aldehyde-contaminated product or by-product. The prior art does not suggest a method for destroying or removing free aldehyde from melamine-aldehyde resin as a part of the process of production of the resin. Additionally, the prior art only suggests methods for removing the free aldehyde which also causes removal of resin, due to the non specific attack on both free aldehyde and resin by the oxidizing agent.
U.S. Pat. No. 4,447,241 to Hendrix et al discloses the use of melamine-aldehyde resins in the treatment of fabrics to impart a durable press characteristic. After treatment of the fabric with the resin, and oven curing of the resin-impregnated fabric, the fabric is contacted with an oxidizing agent to destroy free and releasable formaldehyde. U.S. Pat. No. 4,127,382 to Perry similarly calls for treatment of the resin-impregnated fabric with a free formaldehyde scavenger. See also U.S. Pat. No. 3,957,431 to Pai et al. U.S. Pat. No. 4,612,556 to Moira involves the treatment of microcapsules made with melamine-formaldehyde to remove free formaldehyde. The microcapsules contain image-generating compounds and are used in self-contained pressure sensitive copying materials.
Some prior art does involve direct treatment of melamine aldehyde resins or similar material prior to the use of the resins. For example, in U.S. Pat. No. 4,935,149 to Morse, a free formaldehyde scavenging agent comprised of urea, acetylacetone and/or glyoxal is added to an aqueous solution of melamine-formaldehyde polymer used as a detackifier in a paint overspray control system. In U.S. Pat. No. 3,723,058 to Reinhardt et al free formaldehyde is removed from a solution of methylolated carbamate, subsequently used to treat fabrics, by reacting the free formaldehyde with phthalimide. This method results in the formation of a precipitate.
Use of hydrogen peroxide with or without an iron catalyst to destroy organic contaminates, including formaldehyde, in wastewater is disclosed by the prior art. For example, U.S. Pat. No. 4,340,490 to Junkermann et al involves destroying phenol and formaldehyde in alkaline wastewater by adding hydrogen peroxide and an iron containing compound. U.S. Pat. No. 4,104,162, to Junkermann et al, discloses removal of formaldehyde from alkaline wastewater using hydrogen peroxide and heat. U.S. Pat. No. 3,929,636 to Zumbrunn involves treating aldehyde contaminated alkaline wastewater with hydrogen peroxide and sulfuric acid.